// -*- Mode: C++; c-basic-offset: 2; indent-tabs-mode: nil -*-
/* Copyright (c) 2009, Google Inc.
 * All rights reserved.
 * 
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 * modification, are permitted provided that the following conditions are
 * met:
 * 
 *     * Redistributions of source code must retain the above copyright
 * notice, this list of conditions and the following disclaimer.
 *     * Redistributions in binary form must reproduce the above
 * copyright notice, this list of conditions and the following disclaimer
 * in the documentation and/or other materials provided with the
 * distribution.
 *     * Neither the name of Google Inc. nor the names of its
 * contributors may be used to endorse or promote products derived from
 * this software without specific prior written permission.
 * 
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
 * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
 * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
 * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
 * OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
 * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
 * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
 * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
 * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
 * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 *
 * ---
 * This file is a Linux-specific part of spinlock_internal.cc
 */

#include <errno.h>
#include <limits.h>
#include <sched.h>
#include <time.h>

#include "gutil/linux_syscall_support.h"

#define FUTEX_WAIT 0
#define FUTEX_WAKE 1
#define FUTEX_PRIVATE_FLAG 128

static bool have_futex;
static int futex_private_flag = FUTEX_PRIVATE_FLAG;

namespace {
static struct InitModule {
    InitModule() {
        int x = 0;
        // futexes are ints, so we can use them only when
        // that's the same size as the lockword_ in SpinLock.
        have_futex = (sizeof(Atomic32) == sizeof(int) &&
                      sys_futex(&x, FUTEX_WAKE, 1, NULL, NULL, 0) >= 0);
        if (have_futex && sys_futex(&x, FUTEX_WAKE | futex_private_flag, 1, NULL, NULL, 0) < 0) {
            futex_private_flag = 0;
        }
    }
} init_module;

} // anonymous namespace

namespace base {
namespace internal {

void SpinLockDelay(volatile Atomic32* w, int32 value, int loop) {
    if (loop != 0) {
        int save_errno = errno;
        struct timespec tm;
        tm.tv_sec = 0;
        if (have_futex) {
            tm.tv_nsec = base::internal::SuggestedDelayNS(loop);
        } else {
            tm.tv_nsec = 2000001; // above 2ms so linux 2.4 doesn't spin
        }
        if (have_futex) {
            tm.tv_nsec *= 16; // increase the delay; we expect explicit wakeups
            sys_futex(reinterpret_cast<int*>(const_cast<Atomic32*>(w)),
                      FUTEX_WAIT | futex_private_flag, value,
                      reinterpret_cast<struct kernel_timespec*>(&tm), NULL, 0);
        } else {
            nanosleep(&tm, NULL);
        }
        errno = save_errno;
    }
}

void SpinLockWake(volatile Atomic32* w, bool all) {
    if (have_futex) {
        sys_futex(reinterpret_cast<int*>(const_cast<Atomic32*>(w)), FUTEX_WAKE | futex_private_flag,
                  all ? INT_MAX : 1, NULL, NULL, 0);
    }
}

} // namespace internal
} // namespace base
